External quality control for dried blood spot-based C-reactive protein assay: experience from the indonesia family life survey and the longitudinal aging study in India.

Measurement of C-reactive protein (CRP), a marker of inflammation, in dried blood spots has been increasingly incorporated into community-based social surveys internationally. Although the dried blood spot-based CRP assay protocol has been validated in the United States, it remains unclear whether laboratories in other less-developed countries can generate CRP results of similar quality. We therefore conducted external quality monitoring for dried blood spot-based CRP measurement for the Indonesia Family Life Survey and the Longitudinal Aging Study in India. Our results show that dried blood spot-based CRP results in these two countries have excellent and consistent correlations with serum-based values and dried blood spot-based results from the reference laboratory in the United States. Even though the results from duplicate samples may have fluctuations in absolute values over time, the relative order of C-reactive protein levels remains similar, and the estimates are reasonably precise for population-based studies that investigate the association between socioeconomic factors and health.